Candidate: Jonathan E. Fogle, DVM, has completed a residency in small animal internal medicine at NCSU and is board certified in Veterinary Internal Medicine. Dr. Fogle's short term goal is to obtain a doctoral degree from the Immunology program at NCSU. Dr. Fogle's long term goal is to continue independent lentiviral research that draws from both his clinical veterinary medicine and doctoral research experience. Proposal: A significant fraction of untreated HIV+ patients (progressors) are characterized by CD4+ and CD8+ T cell immune dysfunction. HIV-specific CD8+ effector cells are induced during the acute stage infection, but become non-responsive or "anergic" to antigenic stimulation shortly after induction. We propose that the CD8+ T cell immune dysfunction is the result of "clonal anergy" induced by membrane-bound TGF-beta (mTGF-beta) on virus activated CD4+CD25+ T reg cells that engage TGF-betaRII on the target cell. This hypothesis cannot be addressed in human subjects but rather requires a well-characterized experimental AIDS lentivirus animal model such as FIV. SPF cats will be infected with the NCSU1 isolate of FIV, plasma and PBMC/LN cells will be collected at various times post infection and quantitated for virus burden by ELISA and Real Time-PCR. PBMC/LN will be phenotyped for surface receptors by flow cytometry, and for Foxp3 mRNA by RT-PCR. Treg cells will be assessed for suppressor function by CD4+CD25+ cell depletion and by incubating FACS purified CD4+CD25+ cells with ConA and rFIVgag-stimulated CD8+ T cells and measuring IFNgamma by ELISpot. Ab-blocking experiments will be designed to test the hypothesis that Treg cells from FIV-infected cats anergize CD8+ T cells via mTGF-beta signaling. Purified CD4+CD25+ cells +/- anti-TGF-beta and purified CD8+ cells +/- anti-TGF-betaRII will be co-cultured and Treg suppressor function analyzed by measuring IFNgamma by ELISpot. Critical elements in the TGFbeta/ TGF-betaRII signaling pathway leading to suppression of CD8+ cell function will be analyzed, including Smad 2/3 phosphorylation, up-regulation of Foxp3 and Smad 7, and suppression of IFNgamma mRNA production. HIV is currently estimated to infect more than 37 million people world wide. FIV is a well established animal model of HIV/AIDS. The results of these experiments will have implications on future therapeutic strategies against HIV and FIV, and contribute to our current understanding of Treg cell function.